iommu/dma-iommu: Allow dma_info_to_prot to be used globally

The dma_info_to_prot() function is needed for drivers that
implement their own DMA operation so that the DMA directions
and attributes can be translated to IOMMU page flags, so
make it a global function.

Change-Id: I4d74f193f75801e2d481f3a2ec4044f2da2ae8aa
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>